1. Field of the Invention
The present invention concerns wireless communications, and more specifically, to a method and apparatus for mitigating interference in a wireless communication system including a heterogeneous network.
2. Related Art
Recently, data transmission over a wireless communication network is sharply increasing. A reason can be attributed to the fact that smart phones, tablet PCs, and other new high data-usage devices are coming up and spreading. In order to satisfy high data transmission as required, such technologies as carrier aggregation (CA) and cognitive ratio (CR) for efficiently using more frequency bands and multi-antenna and multi-base station cooperative transmission for raising data capacity in a limited frequency band are attracting attention.
Further, wireless communication networks are evolving to have more accessible nodes. Here, the “nodes” may mean antennas or antenna groups spaced apart from each other by a predetermined distance or more in a distributed antenna system (DAS), but are not limited to such concept. Rather, the term “node” may have a broader meaning. That is, a node may be a macro base station, a pico cell base station (PeNB), a home base station (HeNB), an RRH (Remote Radio Head), an RRU (Remote Radio Unit), a relay, or a distributed antenna (group). As the node density increases, the wireless communication system having the node density may show higher system performance owing to cooperation between nodes. That is, as compared with when each node operates without a cooperation from an independent base station, much better system performance may be obtained when each node is managed by a single control station for transmission/reception so that it is rendered to operate as an antenna or antenna group for one cell.
If each node may perform scheduling and hand over, with its individual cell ID (identifier), then this may be called a multi-cell system. If, a multi-cell is configured with overlapped coverage, this is referred to as a multi-tier network.
The multi-cell system/multi-tier network is sometimes collectively referred to as a heterogeneous network, as well. The heterogeneous network, in contrast to the homogeneous network configured of homogeneous cells, has multiple nodes operated, mixed in a cell or the same network, and this means that the nodes are operated as different types of base stations from each other, rather than as the same type of base station (or cell). For instance, a macro base station with broader coverage and a plurality of pico/femto base stations with narrower coverage in the coverage of the macro base station, and relays, may be used together.
A heterogeneous network has different characteristics of interference from those of the homogeneous network, and a need exists for a method for mitigating such interference.